Blade for a wind turbine

ABSTRACT

A blade for a wind turbine comprising a blade root portion is described. The blade root portion defines an mounting surface for coupling to a hub or extender of the wind turbine and comprises a plurality of first holes provided with an insert, the blade root portion further comprises a mounting flange arranged in the periphery of the mounting surface and provided with second holes, wherein the inserts comprise a first end embedded in the blade root portion and a second end opposite to said first end, the second end protruding beyond the mounting surface of the blade root portion, and wherein the second ends are fitted in the second holes of the mounting flange and the mounting flange is attached to the blade by means of the inserts. Furthermore, a wind turbine rotor comprising such a blade is described. Methods of manufacturing half a wind turbine blade and a whole wind turbine blade are also described.

This application claims the benefit of European Patent Application EP12382235.5 filed on Jun. 11, 2012 and U.S. Provisional PatentApplication Ser. No. 61/682,607 filed on Aug. 13, 2012, the disclosuresof which are hereby incorporated by reference in their entirety for allpurposes.

The present application relates to a blade for a wind turbine and a windturbine itself. It further relates to methods of manufacturing a windturbine blade half and a wind turbine blade.

BACKGROUND ART

The blades in a wind turbine are typically attached, at a blade rootportion, to a rotor hub, either directly or through an extender.

Typically, the blades are made from composite materials: reinforcingfibres may be bonded to one another with a resin and, subsequently,cured to consolidate. Different kinds of fibres (e.g. glass, carbon,combinations) and resins (e.g. epoxy) may be used in different forms(e.g. prepreg, fibre sheets). Such composite materials may not have thestructural integrity to provide a secure fixing mechanism into which,for example, threaded bolts may be directly inserted. It is thus knownfor wind turbine blades to comprise metal inserts or bushings which areembedded in the blade root in a direction parallel to that of thelongitudinal axis of the blade. Studs, bolts or rods can be used incombination with these bushings to achieve a secure connection betweenthe hub or extender and the blade. It is thus important for a blade rootportion to comprise a (circular) mounting surface matching the hub's orextenders' mounting surface.

In general terms a typical manufacturing process of a wind turbine blademay comprise a first step of moulding and curing two separatelongitudinal blade shells made out of composite material and a secondstep of joining together these two blade shells and removing the finalblade from the mould. Alternatively, a complete blade may bemanufactured in a single moulding step.

Although blades are made from composite material in order to reduce itsweight, it is important to consider the fact that a finished blade, madeof composite, still has a considerable weight. Once a blade has beenmanufactured it may remain in storage until the wind turbine is finallyinstalled. Said storage may last from e.g. one month up to one year.

Therefore, a problem derived from above mentioned storage time is thatduring storage, a blade may deform in a blade root portion due to itsown weight. This may cause e.g. an ovalization of a circular blade rootmounting surface.

Another problem, related to the one mentioned above derives fromaccelerating the manufacturing process of the blade. It is becomingcommon practice nowadays to join two blade shells together and removethem from the mould relatively quickly. In these cases, the resin maynot be fully cured yet and the blades may still be relatively soft.Furthermore, composite materials are well-known for shrinking uponcuring. Both things may cause a deformation of the blade root portion ofthe blade that may lead to incompatibilities between the hub and theblade root or to a cumbersome blade mounting process.

In practice, a deformation of the blade root may lead to a morevulnerable attachment at the hub. The attachment holes of the blade rootmay not be completely aligned with the attachment holes of the hub orextender, and the studs or bolts used for connecting the blade to thehub may not be completely centered in their holes. In operation, thesestuds or bolts may be subjected to transverse loads, potentiallyshortening their lifetime and the lifetime of the blades.

For this reason, it is also known to provide e.g. a metal flange alongthe periphery of the annular mounting surface of the blade root portion.Such a flange helps to provide a more even mounting surface forattachment of the blade to the hub. The mounting flange may be attachedto the blade using a plurality of small bolts or screw or adhesives.This however can be rather time consuming, especially when bolts orscrews are being used and it and furthermore, the small bolts or screwsmay add local stresses on the blade root portion of the blade thuspotentially shortening the lifetime of the blade. It may still happenthat deformations occurring during storage, or local deformations causedby the small bolts or screw, cause the holes in the blade on the onehand and the holes in the hub on the other hand to be slightlymisaligned.

Thus, there still exists a need to provide a blade with a robust bladeroot portion such that deformations of its mounting surface areminimized and a robust attachment to a hub or extender of the windturbine can be provided. At the same time it is desirable that such ablade can be removed from the mould before the curing process is fullycompleted in order to speed up manufacturing process and be morecost-effective without losing robustness of its blade root portion.

SUMMARY

According to a first aspect a blade for a wind turbine is provided. Theblade comprises a blade root portion defining a mounting surface forcoupling to a hub or extender of the wind turbine and comprising aplurality of first holes provided with an insert. The blade root portionfurther comprises a mounting flange arranged in the periphery of themounting surface and provided with second holes, wherein the insertscomprise a first end embedded in the blade root portion and a second endopposite to said first end, the second end protruding beyond themounting surface, and wherein the second ends are fitted in the secondholes of the mounting flange and the mounting flange is attached to theblade by means of the inserts.

According to this aspect, the inserts are inserted in the second holesof the mounting flange and at the same they are also embedded in theblade root portion of the blade. This way, the inserts together with themounting flange may constitute a relatively rigid unity working togetheragainst deformation forces acting on the blade root portion thusreducing undesired deformations due to e.g. the blade's own weightand/or due to speeding up the manufacturing process of the blades. Also,the use of such a relatively rigid structure formed by the inserts andthe mounting flange contributes towards speeding up the moulding step ofthe blade as the desired shape and dimensions of the blade root mountingsurface may be better ensured. This contributes to a better attachmentof the blade to the hub (or to an extender) as a mounting surfacefulfilling manufacturing tolerances ensures a proper alignment of theholes of the mounting flange with those of the inserts embedded in theblade root portion of the blade thus enabling proper insertion offasteners for securing the blade to the hub.

In some embodiments, the mounting flange may be attached to the bladeonly by means of the inserts. This way no other fastening means such asscrews of bolts are required to keep the holes of the flange alignedwith the holes of the blade root thus avoiding local stresses on theblade root portion of the blade caused by these screws or bolts.Furthermore, if a further step of joining a mounting flange to a blademay be avoided, the manufacturing process may be faster as the blade canbe taken out of the mould before the curing process is complete.

Different ways of fitting the inserts in the holes of the mountingflange may be foreseen.

In some embodiments, one or more second ends of the internal inserts andan inner side of the corresponding second holes may comprise a straightshape and an inner diameter of the second holes may be slightly smallerthan an outer diameter of the second ends of the inserts. In thesecases, an interference fit between inserts and mounting flange may beachieved by joining these two parts e.g. by shrink fitting.

In some embodiments, one or more second ends of the inserts may comprisean outer surface having a tapered shape. Such a tapered shape incombination with a complementary shape of the second holes of themounting flange may help to ensure a proper and easy fit between bothparts (inserts and mounting flange).

In some embodiments, one or more second ends of the inserts may comprisea protruding element extending in a plane substantially perpendicular tothat of a longitudinal axis of the insert and an inner side of thecorresponding second holes may comprise an indentation in which saidprotruding element can be positioned. This way a hooking connection maybe established between the mounting flange and the inserts which may notneed additional fastening means between both parts.

In some embodiments, one or more second ends of the inserts may comprisea threaded portion and an inner side of the corresponding second holesmay comprise an indentation in which a nut, matching said threadedportion, can be inserted. This alternative may be a different way ofachieving a hooking connection between the mounting flange and theinserts which may not need additional fastening means between them.

In some embodiments, one or more second ends of the inserts may comprisean external thread and an inner side of the corresponding second holesmay comprise a thread that is complementary to the external thread ofthe inserts. This is a further alternative for achieving a hookingconnection between the mounting flange and the inserts which may notneed additional fastening means between them.

Another aspect provides a wind turbine rotor comprising a hub and atleast one blade substantially as hereinbefore described.

A further aspect provides a method of manufacturing a wind turbine bladehalf. The method may comprise the steps of joining a plurality ofinserts to half a mounting flange, arranging the resulting assemblyinserts-half mounting flange together with fibres in a mould,introducing resin in the mould and curing the resin such that theassembly inserts-half mounting flange is joined to the resin a fibres.This way, the assembly inserts-half mounting flange is moulded togetherwith the fibres resulting in rigid attachment flange-blade through theinserts which are also embedded in the blade root portion of the blade.

Additional objects, advantages and features of embodiments of thepresent blade will become apparent to those skilled in the art uponexamination of the description, or may be learned by practice of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular embodiments of the present blade will be described in thefollowing by way of non-limiting examples, with reference to theappended drawings, in which:

FIG. 1 shows a section view of the attachment of a blade root portion ofthe blade to a pitch bearing of the wind turbine according to anembodiment;

FIGS. 2-5 b each show a section view of the attachment insert-mountingflange according to different embodiments;

FIG. 6 a shows a mounting flange according to an embodiment; and

FIG. 6 b shows an assembly of half a mounting flange-inserts accordingto an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a cross-section of the attachment of a blade to a pitchbearing 20 for attachment to a hub of the wind turbine. The blade maycomprise a blade root portion 10 for coupling to a hub of the windturbine through the pitch bearing 20. In this case, the blade rootportion may be substantially annular. The blade root 10 may comprise aplurality of first holes 101 provided with an internal (metal) bushing11. An annular mounting flange 12 may further be provided along aperiphery of an annular mounting surface 102 of the blade root. Saidmounting flange 12 may be provided with second holes 121. The bushings11 may comprise a first end 111 and a main portion 111 a embedded in theblade root portion 10 and a second end 112 opposite to said first end111. Such a second end 112 may protrude beyond the mounting surface 102and may be fitted in the second holes 121 of the mounting flange 12.

The attachment blade-mounting flange may thus be a relatively rigidconnection as the flange is attached to the metal inserts embedded inthe blade root portion of the blade. The holes of the mounting flange121 and the holes 101 of the blade root 10 may thus remain alignedindependently on whether the blade is taken out of the mould before thecuring process is completed and/or the blade has been left in storagefor quite a long time and as mentioned before, this enables a properinsertion of fasteners 13 for securing the blade to the hub.

FIG. 2 shows an assembly mounting flange-bushing according to a firstembodiment in which an outer surface of the second ends 112 of thebushings 11 and an inner side 122 of the second holes 121 of themounting flange 12 may comprise a straight shape. In these cases, aninner diameter d2 of the second holes 121 may be bigger than an outerdiameter d1 of the second ends 112 of the bushings 11. This way, aninterference fit or friction fit may be established between both partsforming the assembly e.g. by using a shrink fitting technique.

FIG. 3 shows an assembly mounting flange-bushing according to a secondembodiment in which an outer surface of the second ends 112 of thebushings 11 may comprise a decreasing outer diameter d2 shape(considering a direction from the first end 111 to second end 112 of thebushing). In these cases, an inner side 122 of the second holes 121 ofthe mounting flange may comprise a complementary shape having adecreasing inner diameter d2 (considering a direction from a side of theflange 124 facing the blade towards a side of the flange 123 facing thehub when the blade is coupled to the hub).

FIG. 4 and its enlarged detail show an assembly mounting flange-bushingaccording to a third embodiment in which the second ends 112 of theinternal bushings may comprise a threaded portion 113 and an inner sideof the corresponding second holes may comprise an indentation 125 inwhich a nut 14 matching the threaded portion 113 can be inserted. In analternative embodiment (not shown), the outer surface of the second endsmay be threaded and an inner side of the corresponding second holes maycomprise a matching thread. With these embodiments, the inserts may befixed to the mounting flange by screwing either the bushings itself orthe nut which result in a rigid attachment between both parts (mountingflange and bushings).

Each of FIGS. 5 a and 5 b shows an assembly mounting flange-bushingaccording to a fourth embodiment in which the second ends 112 of theinternal bushings may comprise a protruding element 15 arrangedextending in a plane substantially perpendicular to that of alongitudinal axis 114 of the bushing and an inner side of thecorresponding second holes may comprise an indentation 125 in which saidprotruding element 15 can be inserted.

FIG. 5 a shows an example in which the protrusion 15 may be provided atthe end point of the second end 112 of the bushing and the indentation125 may be arranged close to a side of the flange 123 facing the hub.This embodiment defines a hooking connection between inserts andmounting flange.

FIG. 5 b shows an example in which the indentation 125 may be arrangedclose to a side of the flange 124 facing the blade.

According to the examples shown in FIGS. 1-5 b the second ends 112 ofthe mounting flange may be fully inserted into the second holes 121,this means that the totality of the flange's height in an axialdirection (see FIG. 2) of the annular mounting flange and the mountingflange 12 may be attached to the blade root 10 by means of said bushings11. It should be understood that the second ends of the inserts may alsobe inserted a different height in an axial direction of the annularmounting flange.

In all previously described cases a further welding point may be addedbetween each insert or bushing and the mounting flange to ensure theirattachment. A welded attachment may also be established.

In all cases the inserts may be arranged along the whole blade rootportion thus radial rigidity of the blade root portion may be improved.

FIG. 6 a shows an annular mounting flange 12 according to an embodimentcomprising two halves 12′, 12″. Each of the two flange halves 12′, 12″may comprise through holes 121 equidistantly distributed along its halfannular surface. The ends of the flange halves 12′ may be complementaryfor easy attachment. A flange halve 12′ may comprise e.g. an indentation125 or similar at each of its ends and the indentations may becomplementary to indentations 126 provided at each of the ends of thesecond half 12″ such that both flange halves 12′, 12″ may be coupledforming an annular mounting flange 12.

In addition to what was shown in FIG. 6 a with respect to the annularmounting flange, FIG. 6 b shows an assembly of half an annular mountingflange 12′ fitted with metal inserts 11′ according to an embodiment. InFIG. 6 b one end 112′ of the metal inserts 11′ may be fitted into thethrough holes 121 of half an annular mounting flange 12′. The same maybe done for the other mounting flange half. The metal inserts 11′ maythus comprise a free end 111′ that may be embedded into fibres formingthe blade root portion of the blade.

The present application further describes a method of manufacturing ablade half comprising the steps of joining a plurality of metal inserts11′ with half an annular mounting flange 12′, then arranging theresulting assembly metal inserts-half a mounting flange together withfibres in a mould, introducing resin in the mould and curing the resin,such that the assembly inserts. The mounting flange half is joined tothe resin and fibres. Such an arrangement can be done in the followingmanner e.g.: positioning prepregs and then curing or arranging fibresfirst and then introducing the resin e.g. by RTM (Resin TransferMoulding).

This way a blade shell comprising half a blade root provided withembedded metal inserts which are also attached to half a rigid mountingflange can be manufactured. Such a blade shell may be taken from themould before the curing process is complete as the assembly metalinserts-mounting flange will maintain the semi-circularity of the bladeshell. Furthermore, joining together two blade shells being manufacturedas described above result in a blade in which deformations of its bladeroot mounting surface are at least partly minimized.

Although only a number of particular embodiments and examples of theinvention have been disclosed herein, it will be understood by thoseskilled in the art that other alternative embodiments and/or uses of theinvention and obvious modifications and equivalents thereof arepossible. Furthermore, the present invention covers all possiblecombinations of the particular embodiments described. Thus, the scope ofthe present invention should not be limited by particular embodiments,but should be determined only by a fair reading of the claims thatfollow.

1. A blade for a wind turbine, comprising: a blade root portion, theblade root portion defining a mounting surface for coupling to a hub orextender of the wind turbine, the blade root portion comprising aplurality of first holes provided with an insert, the blade root portionfurther comprising a mounting flange arranged in the periphery of themounting surface and provided with second holes, wherein the insertscomprise a first end embedded in the blade root portion and a second endopposite to the first end, the second end protruding beyond the mountingsurface of the blade root portion, and wherein the second ends arefitted in the second holes of the mounting flange and the mountingflange is attached to the blade by the inserts.
 2. The blade accordingto claim 1, wherein the mounting flange is attached to the blade only bythe inserts.
 3. The blade according to claim 1, wherein one or moresecond ends of the inserts and an inner side of the corresponding secondholes comprise a straight shape and an inner diameter of the secondholes is slightly smaller than an outer diameter of the second ends ofthe inserts.
 4. The blade according to claim 1, wherein one or moresecond ends of the inserts comprises an outer surface having a taperedshape.
 5. The blade according to claim 1, wherein one or more secondends of the inserts comprises a protrusion extending in a planesubstantially perpendicular to that of a longitudinal axis of the insertand an inner side of the corresponding second holes comprises anindentation in which the protrusion can be positioned.
 6. The bladeaccording to claim 1, wherein one or more second ends of the insertscomprises a threaded portion and an inner side of the correspondingsecond holes comprises an indentation in which a nut, matching thethreaded portion, can be inserted.
 7. The blade according to claim 1,wherein one or more second ends of the inserts comprises an externalthread and an inner side of the corresponding second holes comprises athread that is complementary to the external thread of the inserts. 8.The blade according to claims 1, wherein the inserts are welded to thesecond holes.
 9. A wind turbine rotor comprising a hub and at least oneblade according to claim
 1. 10. A method of manufacturing a wind turbineblade half, the method comprising the steps of joining a plurality ofinserts to half a mounting flange; arranging the resulting assembly ofinserts-half mounting flange together with fibres in a mould;introducing resin in the mould; and curing the resin, such that theassembly of inserts-half mounting flange is joined to the resin andfibres.
 11. A method of manufacturing a wind turbine blade comprisingmanufacturing two blade halves using a method according to claim 10, andjoining the two blade halves.
 12. A wind turbine rotor comprising a huband at least one blade according to claim
 2. 13. A wind turbine rotorcomprising a hub and at least one blade according to claim
 3. 14. A windturbine rotor comprising a hub and at least one blade according to claim4.
 15. A wind turbine rotor comprising a hub and at least one bladeaccording to claim
 5. 16. A wind turbine rotor comprising a hub and atleast one blade according to claim
 6. 17. A wind turbine rotorcomprising a hub and at least one blade according to claim
 7. 18. A windturbine rotor comprising a hub and at least one blade according to claim8.